The emblematic monument of Thessaloniki, was constructed in the early 4th century AD, on the turning point between the pagan with the Christian world, probably as a temple for ancient cult worship or as a mausoleum for Constantine the Great (306-337). This circular, domed building measures 29.80 meters in height, 24.50 meters in diameter, its walls are 6.30 meters thick and can only be compared architecturally to the Pantheon in Rome. It was erected north of the Arch of Galerius, with which it was linked by a processional road. Not long after it was built and during the early years of the long-lived Byzantine Empire (330-1453), the Rotunda was turned into a Christian church with the addition of a sanctuary on its eastern side. The interior was decorated with Early Byzantine (4th- 6th c. AD) wall mosaics of unique artistry and beauty. According to Byzantine texts, the church was dedicated to the Archangels. It was Thessaloniki’s cathedral church (metropolis) between 1524 and 1591, the year in which it was converted to a mosque by the οttoman conquerors. It remained in use as a mosque until the city’s liberation in 1912. Its dedication since that time to Saint George (Agios Georgios) is owing to the small neighboring church of this name.